1. Field of the Invention
The present invention relates to a pressure sensor device for use in an internal combustion engine and, more particularly, to a pressure sensor device of an internal combustion engine for controlling an output value from a pressure sensor during a time period from occurrence of any erroneous output value in a pressure sensor to decision of failure of the pressure sensor, thereby desirably controlling a fuel injection quantity of an internal combustion engine.
2. Description of the Related Art
In an internal combustion engine, according to a fuel injection system of speed density type, a basic fuel injection quantity to be supplied to the internal combustion engine is determined based on outputs from a pressure sensor that detects a pressure in an intake pipe and from an engine speed sensor that detects an engine speed of the internal combustion engine. A basic fuel injection quantity is generally set so that a fuel injection quantity becomes larger as a pressure in the intake pipe comes to be higher.
FIG. 7 is a schematic diagram of a general control device of an internal combustion engine of speed density type. In this drawing, reference numeral 1 designates an internal combustion engine. Numeral 2 designates an intake pipe for inducing air to be sucked into the internal combustion engine 1. Numeral 3 designates an air cleaner for purifying air to be sucked into the internal combustion engine 1. Numeral 4 designates a throttle for adjusting an air quantity to be sucked into the internal combustion engine 1 in association with an accelerator. Numeral 5 designates a throttle opening sensor for detecting an opening θ of the throttle 4. Numeral 6 designates an engine speed sensor for detecting an engine speed Ne of the internal combustion engine 1. Numeral 7 designates a pressure sensor for detecting a pressure in the intake pipe.
Numeral 8 designates an electronic control unit (ECU) including a microcomputer. In the electronic control unit (ECU) 8, outputs from the throttle opening sensor 5, the engine speed sensor 6, the pressure sensor 7 and the like are inputted to the ECU and transmitted through the circuit on the ECU. Further, an analog data is converted to a digital data with an A/D converter. Furthermore, on the basis of those data values, a fuel injection quantity to be supplied to the internal combustion engine, an ignition time, an air quantity at an idle time and the like are arithmetically operated. Numeral 9 designates an injector for injecting a fuel downstream of the intake pipe 2 based on a fuel injection quantity having been operated in the ECU 8.
The pressure sensor 7 includes a plus electrode terminal to which, for example, a voltage of 5V is applied, and a ground terminal to which a voltage of 0V is applied. The pressure sensor 7 detects a pressure in the intake pipe 2, and outputs from an output terminal a voltage of 4V at the time of atmospheric pressure and a voltage of 0V at the time of vacuum pressure. This output from the pressure sensor 7 is inputted to the microcomputer on the ECU as an output value Pout from the pressure sensor via the electric circuit on the ECU.
The output from the pressure sensor 7 is used for arithmetic operation of a fuel injection quantity and the like, and plays a major role for supplying a fuel essential for the internal combustion engine, and therefore an operation state of the pressure sensor 7 is monitored at all times. Determination of whether or not the pressure sensor 7 is in failure is made based on whether or not the output value Pout from the pressure sensor 7 is a value that cannot be taken normally. For example, an upper limit Phigh and a lower limit Plow that an output Pout from the pressure sensor can take under normal conditions are preliminarily set, and the output value Pout from the pressure sensor 7 is compared with these upper and lower limits.
When Pout>Phigh, the failure on the upper limit side of the pressure sensor 7 is determined.
When Pout<Plow, the failure on the lower limit side of the pressure sensor 7 is determined.
For example, according to the Japanese Patent Publication (unexamined) No.293303/1997, in a device for compensating a fuel injection quantity based on the variation of an output Pout from the pressure sensor, the following operations are performed. That is, in case of the pressure sensor being determined as being in failure, an output from the pressure sensor for use in the fuel operation is forced to replace with a dummy value having been preliminarily set. At this time, to prevent compensation of a fuel injection quantity due to change in output from the pressure sensor, any compensation of a fuel injection quantity due to change in output from the pressure sensor is inhibited after the pressure sensor has been determined as being in failure. As an alternative means, an output from the pressure sensor for use in the fuel operation is caused to change by degrees up to a dummy value after the pressure sensor has been determined as being in failure thereby preventing the compensation of a fuel injection quantity due to sharp change in output from the pressure sensor.
However, in the conventional pressure sensor error time control device of an internal combustion engine, the following operations have been executed. For example, in the case where an output from the pressure sensor is inputted to a microcomputer after having been processed with a filter on an input circuit of an ECU, there is a time lag between the occurrence of an erroneous value of the pressure sensor and the determination of failure even if the compensation of a fuel injection quantity is inhibited after any failure has been determined. Further, the basic operation of a fuel injection quantity is executed on the basis of an output Pout from the pressure sensor and an engine speed of the internal combustion engine. As a result, until the determination of failure, the fuel operation is undesirably performed based on an erroneous output value Pout from the pressure sensor, the output value Pout being different from an actual pressure in the intake pipe.
For example, in the case where the pressure sensor shows such a behavior as upper limit-side failure when a throttle opening is in the idle position, as shown in FIG. 2, an output value Pout from the pressure sensor becomes larger gradually due to filter processing in an input circuit of the ECU even if any error occurs in the pressure sensor. Therefore, there arises a time lag between the occurrence of the erroneous output value from the pressure sensor and the determination of failure, and accordingly during a time period until the failure is determined, the fuel operation is performed with an output Pout from the pressure sensor, the value Pout being larger than an actual pressure in the intake pipe. Consequently, a problem exits in that, as shown in the lower chart of FIG. 2, a fuel exceeding an essentially required fuel injection quantity is supplied to the internal combustion engine eventually resulting in a state of over-rich.